Hydroxy-functional acrylate resins of relatively low molecular weight (typically 1000 to 3000) are valuable reactive intermediates for making high-performance coatings and other thermoset polymers. The resins are crosslinked with melamines, isocyanates, or epoxy resins to give useful thermoset polymers.
Hydroxy-functional acrylate resins are typically made by copolymerizing hydroxyacrylate monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, or the like, often with other ordinary acrylate monomers (butyl acrylate, ethyl acrylate, etc.). Resins having sufficiently low molecular weight are difficult to make because acrylate monomers are highly reactive and tend to form polymers of high molecular weight.
To limit polymer molecular weight, resin producers include a large amount of a chain-transfer agent, such as a mercaptan, in the polymerization system. The chain-transfer agent usually remains in the acrylate resin. Other than limiting polymer molecular weight, chain-transfer agents provide no benefit for acrylate resins. In fact, chain-transfer agents add cost, often introduce objectionable odors, and can adversely impact resin performance.
Acrylate resin producers commonly use a solution polymerization to control reaction rates. To get a neat resin, the solvent must subsequently be removed from the resin. Optionally, the resin is sold as a solution, but this limits the utility of the product because formulators may prefer a different solvent than the one used for manufacture.
Hydroxyacrylate monomers, which provide hydroxyl functionality to an acrylate resin, are fairly expensive. Less costly ways to introduce hydroxyl functionality into acrylate resins are of interest.
New hydroxy-functional acrylate resins are needed. Preferably, low-molecular-weight resins could be made without the need to use a chain-transfer agent or a reaction solvent. Ideally, the resins would have both acrylate and hydroxyl functionalities, and would be made from inexpensive starting materials. Also needed are hydroxy-functional acrylate resins useful in high-solids, low-VOC formulations, particularly those having high hydroxyl-group contents and low viscosities. Preferred resins would be useful in a broad array of thermoset polymers, such as polyurethanes, epoxies, and melamines.